Gas-filled discharge tube with gas-refilling means

ABSTRACT

A unit for supplying gas to a gas-filled discharge tube includes a gas container and a reservoir in communication therewith. The reservoir has an outlet portion and valve means are provided at the reservoir outlet to selectively place the reservoir in and out of fluid communication with a chamber. The latter in turn communicates with the interior of the discharge tube.

United States Patent Oikado 1 Feb. 8, 1972 [54] GAS-FILLED DISCHARGETUBE WITH GAS-REFILLING MEANS [72] Inventor: Taizo Oikado, Tokyo, Japan[7 3] Assignee: Nippon Electric Co., Ltd., Tokyo, Japan 22 Filed: June24, 1970 A 7 [2 1] Appl. No.: 49,380

[30] Foreign Application Priority Data June 30, 1969 Japan ..44/52065[52] US. Cl ..313/l75, 315/110, 316/24, 331/945 [51] Int. Cl. ..H01jl7/26,1-101j 61/24 [58] FieldotSearch ..315/108,110;313/l75,180;331/945; 316/11, 24

[56] References Cited UNITED STATES PATENTS 2,009,218 7/1935 Baumhaueret a1 ..3l5/l10 X 1,025,635 5/1912 Machlett ..313/175 3,566,304 2/1971Neusel et a1 ..315/110 X Primary Examiner-Roy Lake AssistantExaminerPalmer C. Demeo Attorney sandoe, Hopgood and Calimafde [57]ABSTRACT A unit for supplying gas to a gas-filled discharge tubeincludes a gas container and a reservoir in communication therewith. Thereservoir has an outlet portion and valve means are provided at thereservoir outlet to selectively place the reservoir in and out of fluidcommunication with a chamber. The latter in turn communicates with theinterior of the discharge tube.

2 Claims, 2 Drawing Figures PATENT Ema a 1972 FIG! INVENTOR. TAIZOOIKADO GAS-FILLED DISCHARGE TllBE WITH GAS-REFILLING MEANS Thisinvention relates generally to gas-filled discharge tubes and, moreparticularly, to an improved laser discharge tube of the kind equippedwith a gas refilling unit.

As is known, the useful life of a gas tube, particularly a laser high asseveral tens of amperes, the gas pressure within the tube decreases at afairly high rate, thereby adversely affecting the life of the tube. Toovercome this difficulty, a fresh supply of gas must be supplied atcertain intervals to the tube interior in response to the decrease inthe gas pressure.

A conventional apparatus employed for this purpose consists of a gascontainer and two electromagnetic valves installed in a tube connectingthe container and the laser tube so that the gas confined in the tubelying between the two valves may be fed to the laser tube by thealternate opening and closing of these valves.

This gas-refilling apparatus has significant drawbacks not only becauseit requires a relatively complex mechanism, but

also because the tube is easily damaged or broken during themanufacturing process, or during shipment because of the use of theheavy electromagnetic valves.

It is an object of the invention to provide a gas tube equipped with asimplified and inexpensive means for gas refilling.

It is a further object of the invention to provide a gas refilling unitfor a gas tube in which gas may be supplied to the tube in an accuratelycontrolled manner to maintain a desired gas pressure within the tube.

According to this invention a gas tube is equipped with a gas refillingunit which is comprised of a main gas container, an intermediate gasreservoir, a chamber directly connected to the interior of a gas-filledtube, and valve means lying between the intermediate gas reservoir andthe chamber. The main container communicates with the reservoir througha thin tube of an extremely small orifice or passageway, such as apinhole formed in a metal plate. This tube establishes an extremelyrestricted flow rate of gas from the main. container to the reservoir.

The valve means may be, as herein specifically described, in the form ofa tapered outlet pipe projecting downward into a recessed portion of thechamber and constituting a part of the inten'nediate reservoir. Alow-melting-point metal or the like is placed in and fills part of therecessed portion sufficient to reach the tip of the tapered pipe. Meansare provided to melt the metal into a liquid state whenever it isdesired to release the gas contained in the reservoir into the chamber.When it is in the solid state, the metal restricts the gas within thereservoir and, at the same time, serves as a part of the tube envelope.

When the metal is melted, only the gas that is contained in theintermediate reservoir is released under the gas pressure of the maincontainer to the interior of the tube. The gas in the main containerdoes not reach the tube at this stage, due to the extremely thin orificelinking the main container and the intermediate reservoir. Thus, asubstantially predetermined quantity of gas is released for refillingevery time the valve is heated and the metal is melted. v

To the accomplishment of the above and to such further objects as mayhereinafter appear, the present invention relates to a gas filleddischarge tube with gas-refilling means substantially as defined in theappended claims, and as described in the following specification takentogether with the accompanying drawing in which:

FIG. 1 is a perspective view of a gas tube for use in a laser; and

HO. 2 is a longitudinal cross sectional view of the gas refilling unitof the invention for use with the tube of FIG. 1.

Referring to H0. 1, a gas laser tube 1 is equipped with a gas refillingunit2 of the invention, the latter serving to replenish the supply ofgas (e.g., argon) in the former whenever necessary to maintain asufficient gas pressure therein. The refilling unit 2 may be connectedby a pipe section 10 to a suitable portion of the sidewall of either endof gas laser tube 1. Both unit 2 and pipe section 10 are placed awayfrom the laser light path in the tube 1. v

The gas-refilling unit 2, as shown in greater detail in FIG. 2, includesa main gas container 3 and an intermediate reservoir 8. A tube 4 havingan extremely fine orifice or passageway effects communication betweencontainer 3 and reservoir 8 and controls the flow rate of gastherebetween. A gas outlet pipe 5 having a tapered'end is provided atone end of intermediate reservoir 8 and protrudes into a recessedportion of a chamber 9,which in turn communicates at its upper end withthe lower end of pipe section 10 and thus with the envelope of tube 1. Alow-melting-point metal 6 such as indium is placed within andsubstantially fills the recessed portion of chamber 9, and a heater coil7 energized by a'power supply 11 surrounds the recessed portion and themetal.

In its solid state, metal 6 forms a hermetic seal for pipe 5 and thusfor tube 1. However, when metal 6 is warmed up by the operation ofheater 7 to a temperature of say 157 C. (melting point of indium), thegas-filling reservoir 8 is released through pipe 5 and the melted metalinto chamber 9. Stated more specifically, the main container 3 ismaintained at a pressure of several ten to several hundred torr. Withthe metal 6 in the melted state, the gas contained in the reservoir 8passes through the melted metal and overcomes the weight orgravitational pressure plus the surface tension of the melted metalthereof. As soon as the gas pressure in reservoir 8 is decreased to apredetermined value less than the gravitational pressure of the meltedmetal lying from the surface to the tip of outlet pipe 5, the gas flowis stopped. Reservoir 8 is then refilled with fresh gas from container 3through the orifice in tube 4.

If the gravitational pressure of the melted metal remains unchanged, thecritical pressure at which gas is allowed to pass therethrough dependsmainly on the surface tension of the melted indium. Although the surfacetension of the indium varies with the orifice diameter of outlet pipe 5,the physical configuration of the orifice, and the wettability betweenthe melted indium and the pipe material, it is roughly in inverseproportion to the orifice diameter of pipe 5. ln other words, the gaspressure at which gas starts penetrating the melted metal is determinedby the orifice diameter of the outlet pipe As will be apparent from theforegoing description, the gasrefilling process iscarried outintermittently. Since the amount of gas introduced into chamber 9 in onerefilling operation can be kept almost constant, the totaL amount of gasfor the recovery of the rated gas pressure at one time is determined bythe number of refilling operations to be repeated.

Furthermore, the amount of gas corresponding to a single refillingoperation can be determined by suitably designing the volume ofintermediate reservoir 8 and the orifice diameter of outlet pipe 5. Thetime interval between two successive refilling strokes can be controlledby suitably determining the gas pressure in main container 3 and thediameter of the orifice of tube 4.

Experiments carried out on the system of the invention have shown thatthe amount of argon gas corresponding to one refilling stroke and thetime interval between two successive refilling strokes were respectivelyabout 40 cubic centimeters torr, and 20 seconds. In the performance ofthese tests on the system, the pressure in gas container 3 was torr; thediameter of the orifice of tube 4 was 30 microns; the volume ofintermediate gas reservoir 8 was 25 cc.; and the orifice diameter of gasoutlet pipe 5 was 2 millimeters. It is to be understood that thesevalues are given only for purposes of example and are in no way intendedto limit the scope of the invention.

The electric heater 7 for the indium can be manually controlled byobserving pressure reading at a gauge (not shown) for detecting the gaspressure. Alternatively, the electric heater may be turned on" and offautomatically by applying a control signal derived from a pressure gaugeto the heater.

In the embodiment, the tube 4 of small orifice is employed as a meansfor moderating the flow of gas from container 3 into reservoir 8. Thissmall orifice may be a pinhole formed in a thin plate to replace tube 4.Moreover, the low-meltingpoint metal 6 may be other than indium. Tin orany other suitable substance of low-melting point may be employed forthe same purpose.

It would also be understood that the gas-refilling means of the presentinvention is applicable not only to a laser discharge tube but to ageneral gas-filled discharge tube.

The gas-refilling means of this invention can be made compact, light,inexpensive, and easy to handle, because the entire structure can bemade of glass.

Thus while only a single embodiment of the present invention has beenherein specifically described it will be apparent that modifications maybe therein without departing from the spirit and the scope of theinvention.

1 claim:

1. A gas-filled discharge tube of the type having a gas-filled chamberrequiring gas refilling at predetermined time intervals, and agas-refilling unit, said gas-refilling unit comprising a container forcontaining gas at a predetermined pressure, an

intermediate reservoir in fluid communication with said container forallowing a limited flow rate of said gas, said intermediate reservoirhaving an outlet portion, means for restricting the flow of gas fromsaid container to said reservoir, said flow restricting means comprisinga tube section for providing a narrow passageway interposed between saidcontainer and said reservoir, the length and the cross-sectional area ofsaid passageway being sufficient to cause at least a temporarydifference in pressure between said container and said reservoir whenthe outlet portion of said reservoir is opened, valve means interposedbetween said reservoir and said chamber and comprising a recess portionprovided in a part of said chamber receiving said outlet portion, aquantity of meltable metal disposed between said recess portion and theopen end of said outlet portion, and means for varying the temperatureof said metal to thereby alter said metal from a solid to a liquidstate, said gas contained in said reservoir passing through the meltedmetal and overcoming the gravitational pressure plus the surfacetensionthereof in its melted state, said gas flow from said reservoir to saidchamber being automatically stopped as soon as the gas pressure in saidreservoir is decreased to a predetermined value less than thegravitational pressure of the melted metal.

2. The combination of claim 1, in which said meltable material is alow-melting point metal selected from the group consisting of indium andtin.

1. A gas-filled discharge tube of the type having a gas-filled chamberrequiring gas refilling at predetermined time intervals, and agas-refilling unit, said gas-refilling unit comprising a container forcontaining gas at a predetermined pressure, an intermediate reservoir influid communication with said container for allowing a limited flow rateof said gas, said intermediate reservoir having an outlet portion, meansfor restricting the flow of gas from said container to said reservoir,said flow restricting means comprising a tube section for providing anarrow passageway interposed between said container and said reservoir,the length and the cross-sectional area of said passageway beingsufficient to cause at least a temporary difference in pressure betweensaid container and said reservoir when the outlet portion of saidreservoir is opened, valve means interposed between said reservoir andsaid chamber and comprising a recess portion provided in a part of saidchamber receiving said outlet portion, a quantity of meltable metaldisposed between said recess portion and the open end of said outletportion, and means for varying the temperature of said metal to therebyalter said metal from a solid to a liquid state, said gas contained insaid reservoir passing through the melted metal and overcoming thegravitational pressure plus the surface tension thereof in its meltedstate, said gas flow from said reservoir to said chamber beingautomatically stopped as soon as the gas pressure in said reservoir isdecreased to a predetermined value less than the gravitational pressureof the melted metal.
 2. The combination of claim 1, in which saidmeltable material is a low-melting point metal selected from the groupconsisting of indium and tin.